Optical waveguides, such as optical fibers and light pipes, are commonly used for transmitting light in applications such as illumination, communications, medical applications, and the like. Light is guided through the optical waveguide by total internal reflection when the angle of incidence is within the acceptance angle, or critical angle, of the waveguide.
Light is typically coupled into a light pipe by illuminating an input end of the pipe. The amount of light that can be coupled into the light pipe is limited by the area of the input end and by the brightness of the source. It is conventional practice to use a lens system to focus the output of a light source on the input end of an optical fiber or light pipe. However, no lens system is capable of increasing the brightness of a source. Furthermore, a portion of the focused light may not be within the acceptance angle of the optical waveguide and thus is not transmitted.
Nonimaging concentrators are frequently used for solar energy collection. A concentrator collects energy over a relatively large area and delivers it to a smaller area. A typical concentrator has a reflecting surface that reflects solar energy to an absorber. Because the concentrator has a limited angular field of view, it is often necessary to move the concentrator to follow the sun. Nonimaging concentrators are described generally by R. Winston et al in "Nonimaging Concentrators (Optics)", Encyclopedia of Lasers and Optical Technology, Academic Press Inc., 1991, pages 319-330. A nonimaging light direction device is disclosed in U.S. Pat. No. 4,237,332 issued Dec. 2, 1980 to Winston.
Prior art light concentrators have reflecting surfaces with profiles which can be described over most of their length with second order functions. That is, the profiles do not have inflection points. Multiple reflections typically occur in the vicinity of the light source. These reflections produce absorptive losses on the order of 10-15% per reflection. The prior art configurations also tend to direct the light into lossy parts of the source and the mounting structure.
It is a general object of the present invention to provide improved devices for coupling light from a light source into an optical waveguide.
It is another object of the present invention to provide a reflector for efficiently coupling light from a light source into an optical waveguide.
It is a further object of the present invention to provide an optical coupler for coupling light from a source into an optical waveguide with low absorptive losses.
It is yet another object of the present invention to provide a double-ended optical coupler for coupling light from a source into two optical waveguides.